1. Field of the Invention
The present invention relates generally to cameras, and more particularly to cameras for producing acceptable quality video data in varying lighting conditions.
2. Description of the Related Arts
One of the challenges for imaging capturing devices is to capture acceptable quality images in a variety of lighting conditions. Most image capturing devices are challenged by very low visible light or no visible light conditions.
Some conventional cameras have a “night mode” which can be used for capturing images in low light conditions. However, some of these conventional cameras simply increase the exposure time in the “night mode”, so as to gather sufficient light in low light conditions. There are several problems with such cameras. For one thing, increase in the exposure time implies that it takes longer to capture each image. This can be unacceptable or undesirable in certain situations, such as in a security/surveillance camera where a delay in capturing an image can result in missed information. This can also be undesirable if a video stream is being captured, since this results in a lower frame-rate. Further, this solution alone still requires a certain amount of visible light to be present, and thus will not function in really low visible light or no visible light environments. Other conventional cameras may use other solutions which also suffer from several problems, and which again require at least a certain amount of visible light, and will not work in extremely low or no visible light environments.
There are some applications where it is critical to produce image (video and/or still) data all around the clock. One such application is a video surveillance camera system. In a 24 hour period, the lighting conditions change from night to day and then day to night again. Video surveillance cameras are often located in environments where the visible lighting is very low or non-existent at night time. It is therefore particularly difficult to produce good video in night conditions. Further, it is not desirable to use a visible light source on a surveillance camera—this may alert intruders, disturb neighbors, etc.
Some existing surveillance cameras have non-visible light sources, such as infra-red (IR) lighting using IR LEDs. IR lighting is invisible to the human eye, so the camera may remain stealthy, and will pose much less of a nuisance to the neighbors. However, such existing cameras have very big pixels so as to not have severe degradation of image quality when using IR. Thus such cameras have very poor resolution and thus produce poor quality images in many lighting environments, including when visible light is present.
IR light poses problems in normal (visible) lighting conditions. In normal lighting conditions, the lens and sensor (imager) in a camera are very sensitive to Infra-Red (IR) light. An imager is very sensitive to IR lighting because of the longer wavelength which penetrates deeper into the imager device substrate than visible light and washes the color out of the scene, creating a black and white picture. This is particularly problematic because in natural light, plenty of IR light is included with all the visible light.
In a cameras of high quality, images captured in adequate light (e.g., in the daytime) should look natural to the users with good color and sharpness, while at the same time images captured in low or no visible light conditions (e.g., night time without sufficient visible light) should also have acceptable quality. In cameras used in very low light scenarios or in no light scenarios (e.g., in a dimly illuminated environment or unlit environment at night), such as surveillance cameras, it is especially important that these cameras work well not only in brightly lit environments, but in such low light environments as well.
Thus there is a need for a camera that functions well not only in well-lit environments, but also in very low visible light or no visible light environments, and where the captured images remain in focus regardless of whether visible light is present or not. Further, it is desirable to have a camera that can function in a gamut of visible light environments, and can be switched from a sufficient visible light mode to an insufficient visible light mode in a simple and intuitive manner. Moreover, an algorithm is needed to determine whether the sufficient illumination with visible light is present and when it is not. Moreover, such a camera needs to have a compact form factor. Further still, such a camera needs to compensate for the different wavelengths and penetrating properties of visible and non-visible light.